This invention relates to the synthesis of non-zeolitic molecular sieves. It more particularly relates to a method of preparing non-zeolitic molecular sieves (NZMS) at low cost and with simplified processing.
The non-zeolitic molecular sieves to which the present invention is directed comprise crystalline, three-dimensional microporous framework structures of tetrahedrally-bound AlO.sub.2 and PO.sub.2 oxide units, and optionally one or more metals in tetrahedral coordination with oxygen atoms. See U.S. Pat. No. 4,861,743. The crystalline aluminophosphate-type materials which are prepared by the present process are useful, inter alia, for a number of catalytic conversion processes, including dewaxing, isomerization, hydroisomerization, hydrocracking, hydrogenation.
A non-zeolitic molecular sieve is prepared from a reaction mixture comprising active sources of the molecular sieve, including active source(s) of aluminum and phosphorous. A preferred active source of alumina in the conventional preparation of the non-zeolitic molecular sieves is an aluminum alkoxide, such as aluminum isopropoxide, or a pseudo-boehmite hydrated aluminum oxide. U.S. Pat. No. 4,310,440, which discloses aluminum phosphate molecular sieves, and U.S. Pat. No. 4,440,871, which discloses silicoaluminophosphates and their preparation, list these sources of aluminum for the preparation of these molecular sieves. These disclosures are completely incorporated herein by reference for all purposes.
U.S. Pat. No. 4,673,559 discloses a hydrolysis method for preparing crystalline silicoaluminophosphates. Useful sources of aluminum oxide taught in '559 include any form of aluminum oxide or hydroxide, organic or inorganic salt or compound. A similar list of aluminum oxide sources is given in U.S. Pat. Nos. 4,877,593 and 4,913,796, which disclose a method of synthesizing a crystalline aluminophosphate using a C.sub.5 -C.sub.7 alkyldiamine directing agent.
U.S. Pat. No. 5,232,683 discloses a method for preparing a crystalline aluminophosphate using a diamine templating agent. Suitable aluminum sources taught in '683 include aluminum oxides such as gamma and beta aluminas, hydroxides as well as mixtures thereof, such as gibbsite, boehmite and pseudo-boehmite or aluminum alkoxides, such as aluminum tri-isopropoxide.
Zhao et al., "Synthesis and Properties of Novel Aluminophosphate Molecular Sieves Produced with Ethylenediamine", Zeolites, 1993, Vol 13, November/December, describes synthesis and properties of AlPO.sub.4 -12 and two reportedly novel aluminophosphates. Aluminum hydroxide, Al(OH).sub.3, was used as the source of alumina in these preparations.
U.S. Pat. No. 5,096,684 to Guth et al. lists aluminum oxides and hydroxides, such as aluminum hydroxide Al(OH).sub.3,! boehmite AlO(OH)! or pseudo boehmite as aluminum sources for preparing SAPO-5, SAPO-11 and SAPO-34. U.S. Pat. No. 5,178,846 to Buelow et al. lists aluminum hydroxide gel and pseudo-boehmite as suitable aluminum compounds to make a wide-pore crystalline aluminophosphate molecular sieve. U.S. Pat. Nos. 5,051,246 and 5,232,683 to Clark, et al. mentions boehmite and pseudo-boehmite in the preparation of aluminophosphates, silicoaluminophosphates and metalloaluminophosphates. U.S. Pat. No. 4,673,559 to Derouane, et al. lists aluminum oxide or hydroxide organic or inorganic salts or compounds as sources of aluminum oxide in the preparation of silicophosphoaluminates.
U.S. Pat. No. 5,230,881 discloses a method for synthesizing substantially pure crystalline SAPO-31. Example methods taught in '881 for preparing both SAPO-31 and other silicoaluminophosphates use pseudo-boehmite (Catapal B and Catapal SB) materials.
A preferred source of alumina in the conventional preparation of non-zeolitic molecular sieves is an aluminum alkoxide, such as aluminum isopropoxide. While other alumina sources have been taught, none have been shown to produce non-zeolitic molecular sieves having catalytic properties, such as catalyst activity and selectivity in the conversion of petroleum and organic feedstocks, equal to that of a non-zeolitic molecular sieve prepared using an aluminum alkoxide as the alumina source. However, aluminum alkoxides are expensive relative to other alumina sources. Furthermore, in the use of aluminum alkoxides in the preparation of non-zeolitic molecular sieves, a waste stream rich in alcohols is produced; this waste stream must be treated or disposed, at additional processing expense. An improved method for preparing a non-zeolitic molecular sieve is desired.